Migrate sanity_check.py into the respective daemons

ucloud/imagescanner/main.py

@@ -18,6 +18,19 @@ def qemu_img_type(path):
         qemu_img_info = json.loads(qemu_img_info.decode("utf-8"))
         return qemu_img_info["format"]
 
+def check():
+    """ check whether settings are sane, refuse to start if they aren't """
+    if env_vars.get('STORAGE_BACKEND') == 'filesystem' and not isdir(env_vars.get('IMAGE_DIR')):
+        print("You have set STORAGE_BACKEND to filesystem, but "
+              "{} does not exist. Refusing to start".format(env_vars.get('IMAGE_DIR')))
+        sys.exit(1)
+
+    try:
+        subprocess.check_output(['which', 'qemu-img'])
+    except Exception:
+        print("qemu-img missing")
+        sys.exit(1)
+
 
 def main():
     # We want to get images entries that requests images to be created